1. Field of the Invention
The present invention relates to a dynamoelectric machine such as an automotive alternator, etc., and particularly relates to a Lundell rotor construction to which permanent magnets are mounted.
2. Description of the Related Art
Automotive alternators that use Lundell rotors have been used in automobiles for decades. Loads from electrical equipment that has been mounted due to environmental issues have increased rapidly in recent years, and further increases in generated power have been sought from Lundell rotors.
If attempts are made to answer these demands within the scope of conventional design, the alternators are invariably increased in size. Increases in the size of alternators are undesirable since the weight of and space occupied by such alternators is increased. Increases in the size of alternators are also known to give rise to new problems such as leading to increased rotor inertia, and engine speed fluctuations and alternator inertial torque interacting and leading to belt vibration and slippage.
Consequently, there is demand to increase alternator capacity while maintaining alternator main body size in its present state.
Conventionally, means of disposing permanent magnets between claw-shaped magnetic poles that face each other in a Lundell rotor have been adopted in order to solve such problems (see Patent Literature 1 and 2, for example).
In a conventional technique according to Patent Literature 1, L-shaped grooves that have an outer circumferential surface that is slightly wider than an inner surface are formed on first and second circumferential end surfaces of claw-shaped magnetic poles, and permanent magnets are inserted into portions of the L-shaped grooves of claw-shaped magnetic poles that face each other in a circumferential direction. The permanent magnets that are disposed between the claw-shaped magnetic poles that face each other in the circumferential direction are prevented by the claw-shaped magnetic poles from moving due to centrifugal force that acts during rotation.
In a conventional technique according to Patent Literature 2, magnetic inserts that are formed so as to have a U shape are disposed between two consecutive magnetic pole fingers of a magnetic pole piece so as to extend below a tip end of a magnetic pole finger of another magnetic pole piece. These magnetic inserts are prevented from moving axially by a cooling fan, and are prevented from moving radially by the overlying magnetic pole fingers.
Patent Literature 1: Japanese Patent Laid-Open No. 2006-74969 (Gazette)
Patent Literature 2: Japanese Patent Laid-Open No. HEI 8-308190 (Gazette)
In automotive alternators of this kind, rotors rotate at high speeds in a vicinity of up to 18,000 to 20,000 rpm when driven by torque that is transmitted from an engine by means of belts and pulleys. Because of this, even if small magnets that weight only a few grams per pole are installed, extremely large centrifugal forces that exceed several tens of kilogram force act on the magnets. Large centrifugal forces also act on the claw-shaped magnetic poles, and the claw tip portions expand approximately 50 to 100 μm radially outward. Thus, the claw-shaped magnetic poles are displaced so as to flap with increases and decreases in engine rotational frequency.
In the conventional techniques according to Patent Literature 1 and 2, because the centrifugal forces that act on the permanent magnets are held by the claw-shaped magnetic poles themselves, which may displace, one problem has been that the permanent magnets may be damaged by the displacement of the claw-shaped magnetic poles, etc., reducing holding reliability for the permanent magnets.
In the conventional techniques according to Patent Literature 1 and 2, because the permanent magnets are disposed in a vicinity of a surface of the rotor, main magnetic flux or leakage flux of the permanent magnets may have components that cannot be kept inside the rotor and that interlink directly with the stator. Thus, induced voltages may arise during no-load de-energization.
In the conventional technique according to Patent Literature 1, due to the action of cooling fans, a portion of a cooling airflow that has been sucked into a case from a front end may flow rearward through the pole core, or a portion of a cooling airflow that has been sucked into the case from a rear end may flow forward through the pole core, and some problems have been that the cooling airflows may interfere with each other, generating loud interference noise, and that the quantity of the cooling airflows may also be reduced, reducing cooling effect.
In the conventional technique according to Patent Literature 2, on the other hand, because the magnetic inserts are disposed between two consecutive magnetic pole fingers of a magnetic pole piece so as to extend below a tip end of a magnetic pole finger of another magnetic pole piece, ventilation channels into the pole core for cooling airflows that have been sucked into the case from the front end and the rear end are blocked. Thus, although interference between the cooling airflows that have been sucked into the case from the front end and the rear end can be prevented, one problem has been that temperature increases in the field coil cannot be suppressed because the cooling airflows are prevented from flowing inside the pole core, reducing cooling effect.